Chemokines are a superfamily of chemoattractant cytokine proteins which primarily serve to regulate a variety of biological responses and promote the recruitment and migration of multiple lineages of leukocytes and lymphocytes to a body organ tissue. Chemokines are classified into four families according to the relative position of the first two cysteine residues in the protein. In one family, the first two cysteines are separated by one amino acid residue (the CXC chemokines) and in another family the first two cysteines are adjacent (the CC chemokines). In a third family, the first two cysteines are separated by three amino acids (CX3C chemokines). In a fourth family there is only one cysteine in the amino terminus (C chemokines).
The molecular targets for chemokines are cell surface receptors. One such receptor is CXC chemokine receptor 4 (CXCR4), which is a seven transmembrane G-protein coupled receptor (GPCR). CXCR4 is widely expressed on cells of hematopoietic origin, and is a major co-receptor with CD4+ for certain strains of human immunodeficiency virus 1 (HIV-1).
CXCL12, formerly known as stromal cell-derived factor-1 (SDF-1), is an alpha or CXC type 7.8 kDa CXC chemokine. CXCL12 is the only known natural ligand for CXCR4, as high affinity CXCL12 binding requires the CXCR4 amino terminus. CXCL12 comprises two closely related members: CXCL12-α and CXCL12-β, the native amino acid sequences of which are known, as are the genomic sequences encoding these proteins (U.S. Pat. No. 5,563,048 and U.S. Pat. No. 5,756,084, both of which are incorporated by reference herein for all purposes).
Originally described as a growth factor for bone marrow developing B cells, CXCL12 was subsequently characterized as a chemoattractant for T cells and monocytes. Genetic ablation of CXCR4 or CXCL12 results in defects in haematopoiesis, vascularization of the intestines, cerebellar formation and heart development. Similar embryonic defects in either of those chemokine receptor or chemokine gene deficient animals has revealed roles for CXCR4-CXCL12 signaling in cardiovascular, neuronal, and hematopoietic stem cell development as well as gastrointestinal vascularization. Previous studies have also established a role for CXCL12 and CXCR4 in gut vascularization, a key process in mucosal immunity and homeostasis. In vitro, CXCL12 stimulates chemotaxis of a wide range of cells including monocytes and bone marrow derived progenitor cells. Particularly notable is its ability to stimulate a high percentage of resting and activated T-lymphocytes.
Consistent with the fact that CXCR4 is a major co-receptor for HIV, CXCL12 has also been shown to block HIV entry into CD4+ cells. CXCR4 is a co-receptor for T-tropic (X4) strains of HIV, which target CD4+ T cells, and CXCL12 can inhibit HIV-1 infection by preventing gp120 binding to CXCR4 and the subsequent gp41 mediated fusion. CXCR4 co-receptor usage correlates with AIDS onset, even though CCR5 is the primary co-receptor for most HIV infections.
Efforts have been made to identify CXCL12-derived peptides that interfere selectively with HIV entry, and not with CXCL12 signaling. A wide range of potential CXCR4 binding fragments of CXCL12 have been proposed for use in blocking HIV infection, indicating that the anti-HIV activity of CXCL12, or fragments of CXCL12, does not depend on antagonism of the CXCR4 receptor.
CXCL12 also directs homeostatic immune cell trafficking and inflammatory responses. Chemokine activation of specific G-protein coupled receptors (GPCR) directs cell migration toward higher chemokine concentration.
Additionally, CXCL12 and CXCR4 mediate cancer cell migration and metastasis. Treatment with CXCR4-neutralizing antibodies reduced metastatic tumor formation in a mouse model for human breast cancer. Subsequently, over twenty cancer types have been shown to express CXCR4 and metastasize to tissues that secrete CXCL12, such as bone marrow, lung, liver and lymph nodes.
CXCL12 and CXCR4 also serve to establish a niche environment for hematopoetic stem cells in bone marrow such that blocking the function of CXCL12 leads to mobilization of said stem cells so that they exit the bone marrow and enter the blood stream.
Accordingly, there is a current need for cost-effective pharmaceutical agents and treatment methods for treating various conditions including autoimmune or inflammation disorders, immune suppression conditions, infections, blood cell deficiencies, cancers and other described conditions and to mobilize stem cells by manipulating and controlling CXCL12 and CXCR4.